This invention relates generally to telemetry systems for physiological implants and more particularly, it relates to a telemetry system for communicating with an implanted cardiac pacer which samples each cycle of a sinusiodal carrier waveform from a telemetry tank for recovering telemetered digital data from the pacer.
Heretofore, there has been proposed in the prior art various telemetry systems for transmitting data into an implanted cardiac pacer as well as systems for signalling out data from the implanted pacer. However, these prior art systems relied upon the use of telemetered data which was required to be in the form of an analog message. As a result, these prior art telemetry systems have a relatively slow telemetry reception rate from the pacer which was generally limited to under 1k baud.
It would therefore be desirable to provide an improved telemetry system for recovering digital data from an implanted pacer at data rates in excess of 1k baud. The telemetry system of the present invention utilizes a sample and hold circuit for sampling each cycle of a sinusoidal carrier waveform from a telemetry tank. Since the electromagnetic field in the telemetry tank is changed in amplitude and frequency due to the loading and unloading of an implanted tank in the pacer, telemetered digital data from the pacer may be recovered by sampling of the carrier waveform as affected by the implanted tank.